BIODEGRADATION OF NAPHTHALENE FROM COAL-TAR AND HEPTAMETHYLNONANE IN MIXED BATCH SYSTEMS

This research presents the first demonstration of substantial microbia l degradation and depletion of naphthalene from coal tar, a multicompo nent aromatic, dense nonaqueous phase liquid (NAPL). The rates and ext ents of microbial degradation of naphthalene from coal tar and from a two-component NAPL simpler in composition than coal tar were evaluated in gently mixed, NAPL-water batch systems. The rate of degradation of naphthalene, the principal constituent in coal tar, was found to be s ignificantly influenced by the rate of external surface mass transfer from the coal tar. Results show that the rate of mass transfer may con trol the overall rate of biotransformation in mixed systems where coal tar is present as a globule (similar or equal to 11 mm diameter). Mas s transfer is relatively rapid and does not limit biodegradation in sl urry systems when coal tar is distributed among a large number of smal l microporous silica particles (similar or equal to 250 mu m diameter) . These results were obtained for conditions favorable for biodegradat ion and provide an indication of the maximum potential rates for micro bial degradation of naphthalene from coal tar. The microbial degradati on process is dependent on relationships between the NAPL composition and the equilibrium aqueous naphthalene concentration, the naphthalene mass transfer rate between the NAPL and the aqueous phases, and the i ntrinsic rates of microbial degradation of naphthalene. These relation ships have been incorporated in a dissolution-degradation framework, a nd the rate-limiting phenomena for the biodegradation process was eval uated using this framework.